With each successive semiconductor technology generation, wafer diameters tend to increase and transistor sizes decrease, resulting in the need for an ever higher degree of accuracy and repeatability in wafer processing. Semiconductor substrate materials, such as silicon wafers, are processed by techniques which include the use of vacuum chambers. These techniques include non plasma applications such as electron beam evaporation, as well as plasma applications, such as sputter deposition, plasma-enhanced chemical vapor deposition (PECVD), resist strip, and plasma etch.
In a typical plasma etch process, plasma density is lower near the edge of the substrate, which may lead to accumulation of a byproduct layer (such as poly-silicon, nitride, metal, etc.) on the top and bottom surfaces of the substrate bevel edge. The byproduct layer may peel or flake off, often onto critical areas of the substrate during transport and succeeding processing steps, thereby leading to lower yield of devices from the substrate. Therefore, it is highly desirable to remove the byproduct from the substrate bevel edge before the substrate goes through the next processing step. One highly effective process is to use plasma to etch away the deposited byproduct on the bevel edge. This process is named plasma bevel etching. An apparatus to carry out this process is a plasma bevel etcher.
Parasitic plasma is undesired during plasma processing of a substrate and can cause contamination due to particles or cause instabilities in the plasma which lead to nonuniform processing. Eliminating parasitic plasma can be difficult as parasitic plasma may form in voids such as hex sockets of hex socket screws, which are widely used in plasma processing systems including plasma bevel etchers. While the hex sockets of the hex socket screws in a plasma processing system could be filled with plugs, such filling renders installation and removal of these screws more difficult and time consuming.